Joints of pipe or tubing used in a well are generally connected end to end and suspended vertically in the well such that each joint of pipe is in tension. The types of force which may act on a body are shear or tangential force, tensile force, and compressive force.
Pressure testing devices of the type disclosed in U.S. Pat. No. 4,067,228 for joints of pipe often include heads which are urged into sealing engagement with opposite ends of the joint of pipe to prevent the escape of pressurized water forced into the pipe. The heads are generally urged by hydraulic or mechanical jacks into sealing relation with ends of the joint of pipe, which puts walls of the pipe in compression. When pressurized fluid is delivered into the pipe, stress in the tubing wall is not an accurate reproduction of the stress in the pipe wall when it is pressurized while suspended in a tubing string.
Some pressure testing devices for joints of pipe or tubing require that threaded caps or plugs be attached to threads on opposite ends of the joint. This type of pressure testing device maintains walls of the tubing in tension while the joint is being pressure tested. However, the use of threaded sealing apparatus is undesirable because of the time required for attaching the sealing devices and because the threaded sealing devices may damage threads on the joint of pipe while they are being connected and disconnected from the pipe.
Pressure testing devices have been developed for relatively thin wall tubing which is pressure tested at low pressures. U.S. Pat. No. 2,610,651 discloses a plug assembly for pressure testing pipe which includes a plug member having a threaded end to receive a hub section of a hand wheel. The hand wheel moves the hub section inwardly toward the pipe section such that a follower is pressed against an annular pressure transmitting member which in turn presses against members until they make contact with each other for compressing and forcing seal rings into sealing engagement with the interior wall of the pipe. The pressure to which the pipe can be tested is limited by frictional forces between the seal rings and the walls retaining the plug assemblies in the pipe which will be overcome by the longitudinal component of fluid pressure within the pipe tending to expel the plug assemblies from opposite ends of the pipe. The patent also discloses a second embodiment which incorporates resilient seal rings which are urged into sealing engagement with the outer wall of the pipe.
U.S. Pat. No. 3,765,560 discloses sealing apparatus for pressure testing a pressure vessel which grippingly engages outer walls of a tubular member for holding an expandable seal in position adjacent an inner wall of the pressure vessel. Fluid pressure urges the expandable seal into sealing engagement with inner surfaces of the vessel. Wedge shaped rings, in sliding relation with inclined surfaces on legs secured to the apparatus, apply force to the outer wall of the vessel for holding the pressure testing apparatus in position.
A long felt need exists for hydrostatic pressure testing apparatus which is capable of testing joints of relatively thick walled tubing to a high pressure, for example 2000 pounds per square inch, while the pipe section is in tension to more nearly simulate conditions to which the pipe section will be subjected in the field under normal operating conditions.